Altitude control for aircraft



Jan. 10, 1939.

B. G. CARLSON ALTITUDE CONTROL FOR AIRCRAFT 2 Sheets-Sheet 1 Filed March 4, 1937 Jan. 10, 1939. B. G. CARLSON 2,143,140

ALTITUDE CONTROL FOR AIRCRAFT Filed March 4, 1937 2- Sheets-Sheet 2 INVENTOR B BerzfGarZsoM Ills AMM Patented Jan. 10, 1939 UNITED STATES PATENT OFFICE Bert G. Carlson, Freeport, N. assignor to Sperry Gyroscope Company, Inc., Brooklyn,

N. Y., a corporation of New York Application March 4,

7' Claims.

This invention relates'tothe control of altitude in automatic pilots for aircraft for causing the craft to fly at a predetermined altitude. More particularly, my invention constitutes an improvement in the altitude control shownin the prior joint application of applicant and Theodore W. Kenyon, Serial No. 107,152, filed October 23, 1936, for Hydraulic automatic pilots.

One of my improvements over the prior appli- 10 cation consists in compensating the barometric control for temperature changes, so that changes is temperature will not aifect the .altitude set- Another important improvement consists 'in 16 ing of the craft in elevation than-shown in the aforesaid p'riorapplication, and which does not involve any follow-back connection between the barometer and the controlled part on the gyro- 20 scope. J

Further advantages of the invention will appear from the following description.

In the drawings, showing several forms my invention' may assume, Fig. 1 is a plan view, partly in section,-of one form of barometric control, with the cover removed. I

Fig. 2 is a vertical section through the same. Fig. 2'A is a transverse section through the control box, taken approximately on broken line 22 of Fig. 2.

Fig. 3 is a plan view, with cover removed, of a modified and preferred form of barometric dev ce.

Fig. 4 is a sectionof the line l4 of Fig. 3.

Fig; 5 is a view of the 35 same, token unbroken interior of a portionof the control box of the automatic pilot, partly in. section and partly in diagram form, and also showing diagrammatically the servo motor rudder control operated therefrom.

Fig. 6 is a detail of the jointed actuating lever of Fig. 3.

Fig. 7 is a detail view showing the shut-of! valve'of Fig. 4 in the shut-off position- Fig.8 is a detailed, side view of the jointed lever, showing the same. in two positions. My invention is shown as applied to an auto matic pilot of the general type shown in prior Patent #1,992,970, dated March 5, 1935,'to E. A. Sperry, Jr., M. F. Bates and Bert G. Carlson, applicant herein. In such gyro pilots, a form gyropendulum or base line -I is usually used as the base for controlling the attitude of the plane fore and aft and laterally. the gyroscope being providing a simpler means for preventing hunt- 1931, Serial No.128,946

c1. za -1a) mounted for oscillation about a fore and aft axis 2 within a gimbal ring 3 which, in turn, is mounted for oscillation about a transverse axis 2'. The ailerons and elevators are controlled through some delicate controls about the two axes of the gyroscope, such as air pick-off devices, and the follow-up connection from the elevator is brought back to the apparatus through the follow-up pulley 5. It is the present practice to enclose the gyroscope and control parts in aclosed casing 41. from which air is continuously exhausted, as

represented by the arrow;

The air pick-oi! means for-elevator control may comprise a semicircular cut-oi! disc I (Fig.

5) secured to move with the gyroscope, and a pair of ports 8 and 9 pivoted on the aircraft on the transverse axis 2' of the gyroscope. The differential pressure drop in the pipes ll and i2 i leading to said ports is used to actuate the main servo motor 90' and elevator 9! through suitable diaphragm 92' and relay valve 92. Normally the position of said ports about axis 2' is governed from the follow-up pulley 5 and also ,by whatever hand adjustment i3 is provided on the pilot. I prefer also to bring in the barometric control diiferentially through these same connections so that the changes of elevation are made through the gyroscope.

As shown in Fig. 5, the bracket l4 supporting the ports 8 and 9 is adjusted about the axis 2' by means of a link l5 pivoted toan arm l6 which is secured to the shaft ll of pinion' l8, rotated from a second pinion l9. On the shaft of the latter is a short bevel gear sector rotated from a bevel'gear2 I, turned from planetary arm 22.01 a differential 23. One side of said difierential is shown as turned from the follow-up pulley 5, while the other side is shown as turned from a worm gear 24 driven from a worm 25 on the shaft of bevel pinion 26, the latter driven from x a bevel pinion 21 on a long shaft 28. Said shaft may be turned directly from the thumb piece l3 to cause the craft to climb ordive, but I also preferably connect the said shaft to a small motor controlled from the barometric means. Said motor isshown as asmall, light, reversible air turbine 29 driven in either direction from air nozzles 30 and 3|, connected to pipes 32 and 32' leadingto-the barometric means 52. Said turbine is shown as comprising a pair of oppositely facing, blade rotors, one foreach nozzle. The turbine is connected through reduction gearing 34 and 35 to drive a worm 36 (Fig. 5,), turning a small worm wheel 31 loosely mounted on the shaft .28, A friction clutch 38 is preferably provided to to the atmosphere.

couple said worm gear to the shaft so that the thumb piece l3 may be turned without turning the air motor and its reduction gearing.

The barometric control proper preferably consists of a flexible container 52 of the type employed in aneroid barometers,but which in this case has a pipe connection 53 which may be opened or closed to the atmosphere at will. As shown, said pipe connection connects with a port 54 in the control box.33, which may be either opened orclosed to the atmosphere by the lateral movement of a slidable cover plate 55, the position of which may be controlled from a thumb piece 56. On the shaft of said thumb piece is shown a lug or pin 5'! engaging a fork 58 in an extension from the top plate.

The nozzles 30, 3| which operate the servo motor 29 are mounted within the casing 41, from which air is being continuously withdrawn. The barometric means, however, is preferably enclosedin a separate casing 59 which is cut off from the main casing 41 and is open at the top The block 33 is shown as having two ports 6|, 6| therein, connected respectively to pipes 32 and 32, and these ports are normally in line with the small slotted openings 62, 62' in the top plate 55 so that, in operation, air is drawn in through said ports and issues from the nozzles 30, 3|. As long as the pressure at both nozzles is equal, the turbine will stand still, but a pressure differential is controlled by a shutter 63 pivoted on axis 64, the movement of which is governed by the expansion and contraction of the barometric container 52.

The shutter 63 is preferably compensated against temperature changes. For this purpose there is shown a bi-metallic strip 63' placed between the shutter and the barometer, said strip having a small knob I on the under surface resting on the expansible container 52. Said stripis clamped at I00 near its other end to the shutter 63 and is designed so that the bending of the outer end of said strip is in the opposite direction to the expansion of the container 52 due to temperature changes.

In' order to prevent hunting ofthe aircraft in elevation, I have shown a means for causing the M ascent (or descent) to cease at the time, or a little before, the craft reaches its predetermined flight level. One. method of accomplishing this is by means of a follow-back connection from the turbine 29 to the barometric means. This is preferably in the form of, a cam 65 shown as mounted on shaft 28 turned from the turbine, against which bears aroller 66 on a lever 61, pinned to cross shaft 68 in casing 59. Also secured to shaft '68 is an arm 68' which is connected by means of a spring 69 to the shutter 63 so that the tension of the spring, and thereby the loading of the flexible container 52, is varied as the turbine 29 revolves one way or the other.

- This means has been found to be very effective in maintaining uniformly level flight and preventing hunting. I

With the plate 55 positioned as shown in Fig. 2-A, the barometric'means is in operation, the port. 55 being at that time closedso that the barometer is sealed. If it is desired .to change the altitude or throw out the automatic means, the handle 56 is merely moved clockwise in Fig. 5, thus moving plate 55 to the right, shutting off the air supply to the nozzles 30, 3| and connecting the pipe 53, and therefore the interior of container 52, to the atmosphere. By this means the barometer can be designed to be sensitive to small changes of altitude, since its range may be made limited.

In the preferred form of barometric control shown in Figs. 3, 4 and 6 to 8, the shutter 63" is shown as in the form of a link pivoted at 10 with its inner end partially overlying the ports 62 and 62' in the control block 33'. Link 63" is shown as actuated through a link II from a lever 12 pivoted at 13 on top of the barometric container 52'. Said lever is shown as pivoted at its left hand end to a bracket 14 secured to a thermostatic bi-metallic strip 15 which is clamped at spaced points l6, l1 and 11' to a relatively heavy strip I8, both strips being fastened by screws I1, 11' to fixed bracket 19.. It 15 will readily be seen, therefore, that the up and down movement of the left hand end of strip 15 will impart a slight motion to the lever 12 and thereby compensate for temperature changes.

90 is a stop bracket to limit the expansion of This construction also has the important advantage of preventing hunting of the craft in elevation, that is, continuous ascent and descent of the craft through a limited range, without the employment of a follow-up device such as shown in Figs. 1, 2 and 5. When the bellows 52 expands on ascent of the craft, the'stop 83 is struck by the right hand end of the jointed lever I2. If the bellows continues to expand, the jointed lever will break in the middle,

as shown in dotted lines in Fig. 8 in exaggerated 40 form, so that the shutter is not moved any further. When, on the other hand, the proper altitude has been reached or slightly exceeded, the lever"|2 will start to move downwardly in Fig. 8 with the joint still broken. This will result in the shutter 63" being moved back to a position to partially close the upper port 62 before said port would have been closed if the lever 12 had not been of this special construction,

' because the return movement is less, so that the ascent or descent will cease by the time the craft reaches the altitude for which it is set instead of afterwards. By this means, any tendency of the airplane to hunt is prevented and uniform altitude maintained. The same but reverse action takes place when the craft is descending, the joint atthis time being broken in the opposite direction.

In this form, also, I have shown the knob 56', which throws the barometric control in and 60 out of operation, as secured to a shaft 64 extending transversely through the control block 33'. Said shaft is shown as threaded therein at 85 and as having transverse bores 86, 86' therein which, when the barometric control is in operation, align with the bores 81, 81' leading to the slots 62, 62' and connected through the pipes 32 and 32'- to the nozzles 30 and 3| on the gyroscope. The valve stem also is shown as made at its lower end in the form of a needle valve .88 7 which normally closes a passage 89 between the interior of the barometric device and the atmosphere within casing 59'. When, however,- the valve is turned to open said passage so as to set the device for a different altitude, as shown in Slightly above the right 25 the device cannot be used to control altitude at this time. It is also obvious that thevalve 88 may be cracked slightly, if desired, instead of being tightly closed, while at the same time leaving the servo motors in operation so that. thevalve will act as a very restricted'opening to the barometer, whereby the barometric means will behave as a rate of climb device, as outlined in my copending Patent #2391306, dated 7 August 31,

1937, for Level flight control for automatic v wall, and differential air ports on each side of the As many changes could be made in the above pilots.

I construction and many apparently widelydifl'erent embodiments of. this invention could be made without departing from the scope thereof, it is intended that all matter contained in the'above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claimand desire to secure by Letters Patent is:

1. In an elevation control for aircraft auto matic pilots, thecombinationlwith servo means {or operating the elevator, ofa barometric device, and a control device operated therefrom for controlling said servo means, said controldevice including a jointed membermoved by the barometer, stops for limiting the movement of one end :thereof' in each direction, and a pick-off device actuated by said member.

2. In a control device for aircraft, the combination with an artificial horizon for controlling the elevator, of a flexible container closed to the atmosphere at will, a shutter connected to the movable side of said container so as to .be moved as said container expands and contracts, an air port on each side of said shutter but out of contact therewith, a pair of oppositely acting air.

motors, one connected to each port, both motors being under the same negative pressure, whereby said motors are diilerentially driven in accordance with the coverage of said ports, controls at the horizon, the relative position of which is altered by said motors, and a single valve for'opening said container and cutting of! said ports from said motors in one operation.

3. In an automatic pilot for aircraft, barometric means of the aneroid type for maintaining a predetermined flight level, an armpivoted adjacent the movable wall of said means, a thernormal position of the shutter for controlling the ascent anddescent of the craft.

5. In an automatic pilot for aircraft, barometric means of the aneroid type for maintaining a predetermined flight level, an arm pivoted adjacent the movable wall of said means, a thermostatic strip secured adjacent one end of said arm and having its other end resting'on said wall, a centralizing spring bearing. at one end against said arm, a movable abutment for the other end u of said spring, means controlled by the movement of said arm in one direction or the other for causing ascent or descent of the craft, and a follow back connection from said means for varying the position of said abutment.

6. In a barometric control device for airplane automatic pilots, a fixed member having three channels therein opening on the same side of said member, an aneroid barometric bellows havnel, a reversible servo motor connected to the other two channels, a plate overlying all of said openings and having a pair of "ports normally registering with the channel openings connected to said servo motor, and also having a port normally out of alignment with the barometric channel, and manual means for shifting said plate,

ing the interior thereof connected to 'one chan- 

